Differential expression of periodontal ligament-specific markers and osteogenic differentiation in human papilloma virus 16-immortalized human gingival fibroblasts and periodontal ligament cells

Background and Objective: Periodontal ligament cells and gingival fibroblasts are important in the remodeling of periodontal tissue, but human papilloma virus (HPV)16-immortalized cell lines derived from human periodontal ligament cells and gingival fibroblasts has not been characterized. The purpose of this study was to establish and differentially characterize the immortalized cell lines from gingival fibroblasts and periodontal ligament by HPV16 transfection. Material and Methods: Cell growth, cell cycle analysis, western blot for cell cycle regulatory proteins and osteogenic differentiation markers, and reverse transcription-polymerase chain reaction for periodontal ligament-specific markers were performed. Results: Both immortalized cell lines (immortalized gingival fibroblasts and immortalized periodontal ligament cells) grew faster than primary cultured gingival fibroblasts or periodontal ligament cells. Immortalized gingival fibroblasts and immortalized periodontal ligament cells overexpressed proteins p16 and p21, and exhibited degradation of proteins pRb and p53, which normally cause cell cycle arrest in G(2)/M-phase. Western blotting and reverse transcription-polymerase chain reaction for periodontal ligament-specific and osteogenic differentiation marker studies demonstrated that a cell line, designated IPDL, mimicked periodontal ligament gene expression for alkaline phosphatase, osteonectin, osteopontin, bone sialoprotein, bone morphogenic protein-2, periostin, S-100A4 and PDLs17. Conclusion: These results indicate that IPDL and immortalized gingival fibroblast cell lines consistently retain normal periodontal ligament and gingival fibroblast phenotypes, respectively, and periodontal ligament markers and osteogenic differentiation in IPDL are distinct from immortalized gingival fibroblast cells.